/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.calcite.sql.validate;

import java.util.ArrayDeque;
import java.util.Deque;

import org.apache.calcite.sql.SqlCall;
import org.apache.calcite.sql.SqlNode;
import org.apache.calcite.sql.util.SqlShuttle;
import org.apache.calcite.sql.util.SqlVisitor;

/**
 * Refinement to {@link SqlShuttle} which maintains a stack of scopes.
 * <p>
 * Derived class should override {@link #visitScoped(SqlCall)} rather than
 * {@link SqlVisitor#visit(SqlCall)}.
 */
public abstract class SqlScopedShuttle extends SqlShuttle {
    // ~ Instance fields
    // --------------------------------------------------------

    private final Deque<SqlValidatorScope> scopes = new ArrayDeque<>();

    // ~ Constructors
    // -----------------------------------------------------------

    protected SqlScopedShuttle(SqlValidatorScope initialScope){
        scopes.push(initialScope);
    }

    // ~ Methods
    // ----------------------------------------------------------------

    public final SqlNode visit(SqlCall call) {
        SqlValidatorScope oldScope = scopes.peek();
        SqlValidatorScope newScope = oldScope.getOperandScope(call);
        scopes.push(newScope);
        SqlNode result = visitScoped(call);
        scopes.pop();
        return result;
    }

    /**
     * Visits an operator call. If the call has entered a new scope, the base
     * class will have already modified the scope.
     */
    protected SqlNode visitScoped(SqlCall call) {
        return super.visit(call);
    }

    /**
     * Returns the current scope.
     */
    protected SqlValidatorScope getScope() {
        return scopes.peek();
    }
}

// End SqlScopedShuttle.java
